I used to feel a lot of resentment towards people who are successful in areas I wanted to be successful, and to some extent, I still do. What changed is that I realized nothing I could have done would have gave me the results I desired for. My mental problems are just too much and they would never allow me to reach the heights I wanted to, not to mention I would still hate the majority of what makes the creature I call "myself". In short, even if I succeeded in the areas I wanted to, I would still be miserable. The truth is was dealt extremely unfavorable cards in this life and it was pretty much impossible for me to become anything I truly desired. No amounts of hard work would lead me there.
So, honestly, I am done feeling bad about cousins and people of my age or younger being "successful" while I am an useless nobody. If they were in my position, I doubt they would have done much. Life wasn't kind to me. I have a broken body and mind and I wasn't even born in a country where opportunities are plenty. It is not fair for me to judge myself based on standards I couldn't possibly meet within my limitations.
Anyways, I can totally relate to what you are saying. I do not agree that being on your 30s is too late to follow a new path, though. It depends on what you want to follow. Certain things you truly need to start as soon as possible, preferably in your childhood, but others not so much. I know people who changed careers after their 30s and are somehow happy and successful, so anything is possible.